This invention relates to a dual backset latch assembly for a cylinder lock, and particularly to an improvement in a dual backset latch assembly which includes two cam members to cooperate with a transmission plate so as to transmit the movement of the spindle of a cylinder lock to a bolt.
Latch assemblies which are adjustable between two backset measurements are available for cylinder locks in the art. These latch assemblies are operable by a spindle of a lock having two knobs respectively provided at the inside and outside of a door. U.S. Pat. No. 4,615,549 discloses a dual backset latch which includes two intersecting cam members which operate about two separate and parallel axes which are the centers of the two spindle backset in common industry usage. In this latch construction, the two cam members are respectively mounted on two side plates of the housing of the latch assembly so as to avoid the interaction of the two cam members during operation. The configuration of the two cam members does not permit the cam members to be mounted on the same side plate of the housing of the latch because one of the two intersecting cam members would obstruct the other when the other is in operation. Since only a pair of cam members can be provided in the latch assembly disclosed in this patent, the latch assembly can cooperate with a lock having a single spindle, but cannot combine with a known lock which has two rotating spindles one of which is operated from the outside of a door and the other of which is operated from the inside of the door.
In addition, the latch assembly described in the U.S. Patent has a disadvantage in that the latch assembly cannot be used in combination with any one of conventional cylinder locks which commonly have two female screws B2 to be secured to the housing of a latch assembly shown in FIG. 1, and is only applicable for a particular cylinder lock having guide plates X which can engage with the housing of the latch assembly shown in FIGS. 1 and 2 and which can be used for the purposes of rigidly connecting the latch assembly to the cylinder lock. This is because no securing hole can be provided in the latch assembly described in the U.S. Patent.